Typical, commercially available carpets, for example continuous-sheeting product or carpet tiles, are manufactured by forming the carpet pile from tufts mechanically inserted, for example in the form of loops, into a woven or laid primary backing. In tufted carpet, the sheet like primary backing holds the loops but loosely, and the loops are therefore treated with a binder-containing formulation to stabilize the unfinished carpet. Said binder-containing formulation is precoated in a foamed or unfoamed state on the reverse side of the primary backing and in addition to an aqueous polymeric dispersion as binder typically further comprises fillers, for example chalk, and optionally further added substances, such as thickening agents, dispersing assistants or foaming assistants.
To improve their dimensional stability, the carpet products thus obtained may be provided a further, secondary backing. The secondary backing generally comprises a woven fabric in a manufactured fiber, such as polypropylene, polyamide or polyester, or in a natural fiber, such as jute. The secondary backing is attached to the as-precoated carpet by again applying a binder, the formulation of which may be similar to that of the coating material for the precoat. Again, in this second coating, the aforementioned aqueous polymeric dispersions, formulated as a foam or in an unfoamed state, may be applied together with fillers and further added substances, such as thickening agents, dispersing assistants or foaming assistants, to form a secondary coating.
WO 90/00967 A1 describes the use of aqueous dispersions of vinyl acetate-ethylene copolymers, styrene-butadiene copolymers or styrene-acrylate copolymers instead of PVC plastisol as binders in carpet manufacture. U.S. Pat. No. 3,779,799 describes the manufacture of a tufted carpet wherein the precoat used comprises binder compositions where the binder is a vinyl acetate-ethylene copolymer dispersion (VAE copolymer dispersion), a polyethylene dispersion or a dispersion of a carboxylated styrene-butadiene copolymer. U.S. Pat. No. 4,239,563 describes aqueous vinyl acetate-ethylene copolymer dispersions useful as binders for consolidation of carpets. The lower emission of volatile organic compounds (VOCs) as compared with styrene-butadiene lattices is emphasized. U.S. Pat. No. 4,735,986 describes a carpet binder comprising a composition comprising a vinyl acetate-ethylene copolymer dispersion comprising a stabilizer mixture of partially hydrolyzed PVOH, fully hydrolyzed PVOH and a nonionic, polyalkoxylated emulsifier. U.S. Pat. No. 5,026,775 described carpet coating compositions based on vinyl acetate-ethylene copolymer dispersions wherein the copolymers further contain monomer units whose homopolymers have Tg glass transition temperatures of at least 50° C. U.K. patent GB 1,298,155 describes carpet coating compositions based on aqueous crosslinkable binders comprising vinyl acetate-ethylene copolymers, polyvinyl alcohol (PVOH) and glyoxal. WO 2010/089142 A1 discloses a vinyl acetate-ethylene copolymer dispersion employed as a binder in carpet manufacture. The copolymer contains from 1 to 4 wt % of ethylene and is emulsifier stabilized only, although small amounts of protective colloid may be co-used for stabilization if necessary. A vinyl acetate homopolymer was tested as a comparative binder. The latter led to carpets of excessive stiffness and unsatisfactory breakage at 180°. To improve adherence to polyvinyl butyral sheeting (as secondary backing), WO 2006/007157 A1 proposes employing a vinyl acetate-ethylene copolymer further comprising from 10 to 10 wt % of comonomer units containing functional groups, such as carboxyl, amide, N-methylol or hydroxyalkyl groups. The copolymer is prepared using a mixture of emulsifier and from 0.05 to 4 wt % of protective colloid. U.S. Pat. No. 6,359,076 proposes improving the water resistance of carpet coatings by employing, in combination with a crosslinker, crosslinkable vinyl acetate-ethylene copolymers which include OH-functional monomer units. WO 2011/139267 A1 and WO 2011/140063 A2 teach carpet coatings based on vinyl acetate-ethylene copolymers comprising functional, crosslinkable comonomer units, such silane-functional or multifunctional comonomers, and not protective colloids but emulsifiers for stabilization purposes. WO 2012/020319 A2 or WO 2012/020321 A2 discloses carpets notable for low flammability or good washability. The binders used were vinyl acetate-ethylene copolymer dispersions having an average particle size dw of 50 to 500 nm, prepared by polymerization under emulsifier stabilization, although up to 3% of protective colloid may additionally be used as a costabilizer if necessary. WO 2013/003547 A2 relates to carpet binders having an optimized composition for formulations with carbon black as a filler. The binders used are vinyl acetate-ethylene copolymer dispersions stabilized with emulsifier and cellulose ether.
WO 2013/123210 A1 relates to carpets manufactured using binder mixtures formed from vinyl acetate-ethylene copolymer dispersions and styrene-butadiene copolymer dispersions. A proposal to improve the compatibility of the various polymeric dispersions involves eschewing polyvinyl alcohol in the VAE dispersion, and at most employing up to 1.5 wt % of polyvinyl alcohol, based on comonomers, as a protective colloid in the preparation thereof. WO 2014/031579 A2 relates to carpet coating compositions which by way of binders may include inter alia VAE dispersions which are emulsifier stabilized and may additionally contain if necessary up to 1.5 wt % of polyvinyl alcohol as a costabilizer. These dispersions are blended with an alpha-olefin-carboxylic acid copolymer and a crosslinker.
There is a need to further develop the properties of vinyl acetate-ethylene-based binders to formulate performance-balanced carpet coating compositions. An attempt in this regard is represented by the binder blends already referred to in WO 2013/123210 A1 which are based on vinyl acetate-ethylene copolymer dispersions and styrene-butadiene copolymer dispersions. Blends of this type are notable for high tuft withdrawal values in the binder mixtures used. However, the vinyl acetate-ethylene copolymer dispersion always contains an emulsifier, which has an adverse effect on filler compatibility and mechanical strength, especially the delamination resistances. Purely protective colloid-stabilized vinyl acetate-ethylene copolymer dispersions, for example with partially saponified polyvinyl alcohol or modified and/or unmodified celluloses, have by contrast good filler compatibilities and high mechanical, strengths, yet generally they are less compatible with styrene-butadiene copolymer dispersions and when included in mixtures absent specific emulsifiers and/or substantial dilution have a proclivity for coagulation or drastic increases in viscosity.
The use of vinyl acetate-ethylene copolymers as binders in secondary backings does provide control over the strength setting of the final carpet, through control of the glass transition temperature of the polymer, yet certain settings remain unattainable nonetheless. Particularly high strengths are but difficult to achieve and aligning the binder to the requirements of the end product while allowing a wide scope for varying the strength would lead to a commercially unattractive multiplicity of products. There is therefore a need for a product which allows the strengths in the ready-produced carpet to be established with mixed-stabilized (emulsifier as well as protective colloid) or purely protective colloid-stabilized vinyl acetate-ethylene copolymers while eschewing plasticizers or film-forming assistants and improves the mechanical strengths of the secondary backing binder comprising vinyl acetate-ethylene copolymer.